1. Field of the Invention
Example embodiments generally relate to a development device, a process unit, and an image forming apparatus, and more particularly, to a development device for supplying developer to an image carrier, and a process unit and an image forming apparatus including the development device.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image carrier; an optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data; a development device supplies toner to the electrostatic latent image formed on the image carrier to make the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image carrier onto a recording medium or is indirectly transferred from the image carrier onto a recording medium via an intermediate transfer member; a cleaner then collects residual toner not transferred and remaining on the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
FIG. 1 illustrates a development device 6R included in such image forming apparatus. In the development device 6R, a toner agitator 5R is rotatably provided in a toner hopper 7R to rotate and agitate developer including toner in the toner hopper 7R. A supply roller 4R rotates in a rotation direction identical to a rotation direction of a development roller 3R to supply the toner in the toner hopper 7R to the development roller 3R. A front edge of a blade 2R, which contacts and presses against the surface of the development roller 3R serving as a developer carrier forms the toner adhered to the surface of the development roller 3R into a uniform thin toner layer. The development roller 3R contacts a photoconductor 1R and transfers the toner forming the thin toner layer on the development roller 3R onto the surface of the photoconductor 1R, where the transferred toner is attracted and adhered to an electrostatic latent image formed on the photoconductor 1R serving as an image carrier. Thus, a toner image is formed on the photoconductor 1R for ultimate transfer to a recording medium to form a final image.
In the development device 6R, the state of contact between the development roller 3R and the photoconductor 1R is critical to proper image formation. If the development roller 3R separates even momentarily from the photoconductor 1R, the development roller 3R does not transfer the toner to the photoconductor 1R properly, resulting in formation of a faulty toner image. By contrast, when the development roller 3R is pressed against the photoconductor 1R strongly, an excessively solid toner image is formed on the photoconductor 1R.
To address this problem, the development device 6R may include a biasing member 8R to press the development roller 3R against the photoconductor 1R at constant pressure, as illustrated in FIGS. 2A and 2B. Bearings 9R are provided on both ends of an axle or shaft of the development roller 3R. The biasing member 8R, which may be a spring, presses against the bearing 9R, which in turn presses the development roller 3R supported by the bearing 9R against the photoconductor 1R. With such an arrangement, the development roller 3R adjusts a distance between a shaft of the photoconductor 1R and the shaft of the development roller 3R to maintain constant pressure of contact between the development roller 3R and the photoconductor 1R, for example, when the distance between the shaft of the photoconductor 1R and the shaft of the development roller 3R is shorter, as is a distance D1 illustrated in FIG. 2A, or longer, as is a distance D2 illustrated in FIG. 2B. Accordingly, even when rotation of the photoconductor 1R or the development roller 3R is eccentric or either one of these members is misshapen, the development roller 3R is still pressed against the photoconductor 1R with constant pressure.
The development device 6R may further include a U-shaped guide 10R as illustrated in FIGS. 3A and 3B, with the bearing 9R movably provided inside the guide 10R. As illustrated in FIG. 3B, when the development roller 3R rotates, a force F generated in accordance with rotation of the development roller 3R causes the bearing 9R to contact an interior wall of the guide 10R. The bearing 9R slides over the interior wall of the guide 10R as the distance between the photoconductor 1R and the development roller 3R changes.
However, the bearing 9R sliding over the interior wall of the guide 10R generates friction between the bearing 9R and the guide 10R. When the friction is greater than the force applied by the biasing member 8R or when the friction prevents the bearing 9R from sliding over the guide 10R smoothly, the development roller 3R may lose contact with the photoconductor 1R momentarily, resulting in formation of a faulty toner image as described above.
To counteract this problem, the biasing member 8R can be made to apply greater force to the bearing 9R. However, the greater force may press the development roller 3R against the photoconductor 1R with greater pressure, resulting in a shortened service life for the photoconductor 1R due to excessive wear and formation of a faulty toner image due to degradation of toner carried by the photoconductor 1R.